The present invention relates generally to operations performed and equipment utilized in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a direct proportional surface control system for a downhole choke.
Many control systems are available for controlling actuation of downhole well tools. Unfortunately, these existing control systems are typically very complex and, therefore, expensive and susceptible to failure in a hostile, corrosive, high temperature and debris-laden well environment.
Furthermore, most existing control systems leave an operator at the surface unsure of the actual position of a downhole actuator. The operator may be provided with an indication of where the downhole actuator should be based on pressure levels, number of pressure applications, etc., but no direct physical indicator is provided to the operator of the actuator's actual position.
In typical open-loop hydraulic control systems, hydraulic fluid is delivered to one side of a piston by a pump, and fluid is discharged from the other side of the piston to a reservoir, usually at atmospheric pressure. One disadvantage of such open-loop hydraulic control systems is that gas entrained in the fluid at low pressures (e.g., at atmospheric pressure) causes non-linear changes in volume as the pressure is increased (e.g., by use of a pump). Such non-linear changes in fluid volume produce uncertainty in the resultant displacement of the piston.
Therefore, it may be seen that improvements are needed in systems for controlling operation of remotely located tools. It is an object of the present invention to provide such improvements.